Renewable resources such as biomass, municipal solid waste (MSW) and triglycerides derived from plants and animals can be used to produce distillate transportation fuels such as a diesel fuel and jet fuel. There is significant art associated with the use of biomass, MSW and renewable fats and oils as feedstocks for producing various high value chemicals and transportation fuels. Conventional processing routes for cellulose based materials typically include gasification and subsequent conversion to targeted chemicals or transportation fuels using conventional technologies, such as Fischer-Tropsch synthesis associated with syngas conversion to liquids. In order to produce a finished product, additional process steps, such as hydroprocessing, must be performed. Consequently, a biomass conversion facility needs to be designed much like a petroleum refinery, or complex chemical plant, that includes processing steps that optimize the quality of the desired end products.
Municipal solid waste conversion plants must be substantially smaller than conventional petroleum refineries because of the nature of the feed. Transporting municipal solid waste over distances greater than about 40 to 50 miles adds excessive cost, unless a specialized network (i.e. rail) is available. Furthermore, these smaller plants (<2000 tons per day) are less efficient and subject to supply disruptions because of fluctuations in local availability of feed.
Further, the gasification of refuse derived fuel to produce a synthesis gas that is acceptable for the production of commodity chemicals or transportation fuels is challenging. Typical biomass and MSW gasifiers available today operate in a non-slagging mode that limits their operating temperature to less than about 2000° F. However, because cellulose-based materials undergo soot formation reactions associated with pyrolysis, operations at elevated temperatures, or high steam levels, is desirable. Elevated temperatures (>2000° F.) help prevent soot formation but can lead to other problems associated with slagging and the vaporization of the inorganic constituents in the cellulose feed matrix. One method to eliminate excessive soot formation is to operate at higher steam to carbon feed ratios. The higher steam levels help mitigate soot formation but has the disadvantage of producing a syngas containing a higher H2/CO ratio than is typically desired for the production of most commodity chemicals and transportation fuels, such as methanol and distillate fuels, such as diesel and jet fuels.
The conversion of triglycerides to diesel and jet fuel is also known in the art. The mass yield of representative triglyceride feeds to diesel fuel is generally about 60% or less and the yield to jet fuel product is lower. These relatively low yields are partly due to the inherent inefficiencies associated with converting the n-alkanes derived from triglycerides (typically C16 to C22) into isomerized, or branched, alkanes having the carbon number range of the targeted products. The conversion of Fischer-Tropsch liquids into diesel and jet fuel products is also known in the art. Typical yields are in the range of about 70-80% for diesel and about 55-70% for jet fuel.
Product efficiency and overall thermal efficiency of a biomass to liquids conversion facility is strongly dependent upon site location. For example, facilities that are adjacent to high users of heat energy have the advantage of being able to export by-product energy. This export energy increases the overall efficiency and economics of the facility. Facilities that cannot export energy have lower efficiencies and thus must improve the overall economic viability of the plant in other ways. Consequently, there is a need in the art for ways to increase the overall economic viability of biomass facilities that have no opportunity to export energy.
There is also a need in the art for cost effective processes for producing transportation fuels from biomass feeds, such as triglycerides and municipal solid waste.